Viscose process for the manufacture of low-shrink rayon



July 24, 1962 R. L. MITCHELL ETAL 3,045,082

VISCOSE PROCESS FOR THE MANUFACTURE OF LOW-SHRINK RAYON Filed Dec. 27,1960 L L E wmw STIT S m fl 5 TANHKW TN mm z m Wm w 3% @mm Mt oziwmo 2 M6255 2 m G 2 @2522; @2223 53% oh @259; wzjdza 92 Q wzfiiim -ma wziSo295% 55x5 E355 :2; D D D @2225 1055b 00 x lj 3,04%,082 Patented July 24,1952 3,046,032 VISCGSE PRQCESS FOR THE MANUFACTURE OF LZBW-SHRRNK RAYONReid Logan Mitchell and Delrnont K. Smith, Morristown,

and Ralph C. Welton, Morris Plains, N.J., assignors to RayonierIncorporated, Shelton, Wash, a corporation of Delaware Filed Dec. 27,1960, Ser. No. 78,779 7 Claims. ((11. 18-54) This invention relates tothe viscose process, and has for its object the provision of an improvedregenerated filament and staple fiber from which low-shrinking fabricscan be formed, and an improved process for producing the filaments andstaple fibers. The invention produces regenerated cellulose filaments(known as rayon) that shrink less than cotton which may be consideredpractically shrink-free only after sanforia ng. This is accomplishedwithout sacrificing the desirable qualities of rayon, such as highstrength, flex and abrasion toughness,

easy dyeability, moisture absorbency, good color, soft hand, excellentuniformity, etc.

Numerous attempts have been made previously to produce an acceptablewashable rayon, but such attempts have failed, due either to the factthat freedom from progressive shrinkage was not obtained or because theshrinkresistant character was accompanied by deterioration in otherproperties that rendered the fiber unusable. Such low-shrink rayon asmade with resin applications or other devices has been impracticablebecause of brittleness, poor hand, and low strength and wear resistance.The invention overcomes the difficulties which have made the productionof washable rayon heretofore impracticable. The improved rayon can besubjected to repeated and severe laundering with practically noshrinkage and without sacficing the other desirable properties of rayon.

In the course of our experimental investigations we discovered a processfor producing low-shrink filaments and staple fibers which can be formedinto washable fabrics having amazing dimensional stability inlaundering. The invention is based upon a system of regenerative-fixingsubsequent to a very high amount of primary stretch followed by completerelaxation.

The invention is carried out by the spinning of viscose under conditionswhich result in filaments having an appreciable amount of skin, mostadvantageously by producing filaments which are nearly or entirelyallskin, and to this end the spinning is under preferred conditions ofretarded regeneration needed to produce the desired skin effect. Theviscose filaments are spun into an acid regenerating bath and aresubjected as soon as possible to a primary stretch of at least 90%,preferably a multistage stretch while in contact with strong acid spinbath carryover, at a preferred temperature of from to 70 C., and thefilaments are then subjected to a secondary stretch of at least 20% in adilute acid bath to complete regeneration. The completely regeneratedfilamenfs are subject to a relaxation treatment in a suitable liquidmedium which causes the filaments to swell, such as by immersion in ahot dilute alkaline solution of sodium hydroxide, potassium hydroxide,lithium hydroxide, sodium carbonate, sodium sulfide, or potassiumthiocyanate. This relaxation treatment, accompanied by the entirecontrolled and progressive stretching, removes any internal structuralimbalances that would contribute to the capacity of the filaments toshrink in water as in laundering. When staple fibers are to be formedwhich is an important variation ofrthe invention, the regeneratedfilaments prior to Washing are cut into staple fibers and the mass ofsuch fibers is washed and then immersed, preferably in a hot dilutesolution of sodium hydroxide for a shorttime. A preferred treatment isto immerse the fibers in an aqueous solution containing about 1% sodiumhydroxide at about 90 C. for a short time, say, about one to fiveminutes, and then wash and finish the filaments in the conventionalmanner. In carrying out a process of the invention, we may use anysuitable viscose composition in any of the Well known procedures forforming rayon filaments having a structure that is substantiallyall-skin. The types of acid regenerating spin baths widely used aresatisfactory such as a modified Mueller bath, preferably underconditions when either the viscose or the spin bath contains an activeregeneration retardant to insure the formation of an effective highproportion of skin.

It is preferred, in forming the viscose, to use cellulose xanthatehaving a uniform chain length at a degree of polymerization of from 300to 800, derived from such cellulose as, for example, Rayocord-X,Cordenier-J, Cor denier-X, of Rayonier Incorporated, or other high-alphacellulose pulps, prehydrolyzed kraft, cotton linters, resinfree pulp,cold-caustic refined pulp, high purity pulp of a high degree ofpolymerization (DP) and uniform chain length, and preoxidized pulp ofhigh purity low DP and uniform chain length.

The process may be carried out with conventional viscose compositionscomprising about 7.5% of cellulose and 6.5% of sodium hydroxide, or inany suitable proportions of cellulose to sodium hydroxide varying from4% to 13% of cellulose and from 5% to 13% of sodium hydroxide such asthe following:

5.0% cellulose and 5.0% caustic soda 6.0% cellulose and 5.0% causticsoda 6.5% cellulose and 7.5% caustic soda 7.5% cellulose and 6.5%caustic soda 8.0% cellulose and 7.0% caustic soda 9.0% cellulose and6.0% caustic soda 9.6% cellulose and 5.0% caustic soda 10.0% celluloseand 5.0% caustic soda 10.0% cellulose and 7.0% caustic soda 13.0%cellulose and 13.0% caustic soda The viscose solution may be preparedaccording to the usual practice to have a salt (sodium chloride) indexvarying from 4 to 20, by xanthating the alkali cellulose with thedesired amount of carbon bisulfide, say, about of the bisulfide. One mayxanthate with the usual 34% of carbon bisulfide and then add to themixed viscose an additional amount of carbon bisulfide to bring it tothe desired sodium chloride index. It is also preferred to spin theviscose into a spin-bath containing from 7 to 10% of sulfuric acid (H 80at a temperature of from to C., and to stretch the filaments undercontrolled conditions while in contact with the spin-bath or spin-bathcarryover. When the usual type of acid-spin bath is used there areadvantages in reducing the salt index, say from 14-20 to 10-12, the H inthe spin bath from 913% to 710%, and the ZnSO from 6-12% to 1-6%.

The copending patent application of Mitchell, Berry and Wadman, SerialNo. 810,991, filed May 5, 1959, and now Patent No. 2,942,931, describesthe addition to viscose of physical mixtures of polyethylene glycol anddimethylamine, preferably in equal amounts of from 0.05 to 0.5% eachbased on the weight of the viscose to control the regeneration andproduce all-skin filaments at especially attractive hi h windup speeds.We may use the process of said patent application up to and includingthe initial or primary stretch.

The spinning operation is carried out in the process and a suitable acidbath to stretch the filaments initially while in contact with the spinbath at least preferaby about but usually not over about Then thefilaments are led into a dilute hot acid. bath containing from 1-6%,preferably about 4%, of sulfuric acid at from 80 C. to 100 0, preferablyabout 90 C., to stretch them an additional 5% to 50%, preferably about30%, to fix the crystal structure and to complete regeneration. Thisdilute hot bath is uesd to dilute the filament salt content to permitfurther stretch and to decompose and remove the last traces ofxanthates. It merely tolerates the adhering or residual salts from theprimary spin bath as the important agent is the hot dilute sulfuricacid.

The regenerated filaments may be superficially washed with hot water andsubjected to the relaxation treatment. After washing they may be cutinto staple fibers, opened,

washed and contacted with the swelling agent, for example dilute causticsolution containing from 0.1% to 2%, preferably about 1%, of sodiumhydroxide, at a temperature varying from 80 C. to 100 C. for a shorttime, say, about one to five minutes to effect complete relaxation.Solutions of other swelling agents may be used as follows: potassiumhydroxide 1.4%, lithium hydroxide 0.6%, sodium carbonate sodium sulfide3.0% and potassium thiocyanate 3.0%

The accompanying drawing is a fiow sheet illustrating a typicaloperation carried out for the production of staple fibers according tothe invention. It is to be understood that in the production ofcontinuous filaments the cutting operation is to be omitted.

The following examples illustrate operations carried out in accordancewith the process of our invention to produce the improved washable andlow-shrink regenerated filaments:

Example I A viscose of 7.5% cellulose and 6.5% sodium hydroxide contentwas prepared from Cordenier-J wood pulp containing 96.6 alpha cellulose,having an intrinsic viscosity of 6.0, degree of polymerization of 1140,and General Electric brightness of 89. The viscose, modified by additionat the mixing stage of 0.1% (based on the Weight of the viscose)dimethylamine and 0.1% polyethylene glycol (M.W. 1540), was extruded at10.0 sodium chloride index through an 1100-hole spinnere'tte into a spinbath comprising 7.8% sulfuric acid, 16% sodium sulfate and 6.0% zincsulfate. The filaments were led through a bath-fed tube for 26 inches,combined with other lIOO-filament yarn ends and with strong primary bathstill clinging thereto given a 5-stage progressive primary stretch of100% with tension build-up to about one gram/denier maximum while stillin an incompletely regenerated, plastic state. The filaments were thenled into a dilute, 4% sulfuric acid bath at 90 C. to impart a secondarystretch of an additional 30% at a tension of about one g./denier and tofix by completing regeneration. The regenerated filaments were led ontoa thread advancing drum showered with hot water to provide a preliminarywash, and then under a low tension of about 0.1 g./ denier wound up at90 meters/minut on a cone with zero twist.

Cones of this yarn were pulled as a tow into a staple cutter to convertthe tow into 1 /2 inch length staple, flowed down a stepwise chute withwater to open, collected on a screen for washing and finishing.

The out staple of 1 /2 inch length and 1 /2 denier per filament wasplaced in a wire basket, washed by displacement through the mat toremove acid. The mat of staple was then given a complete relaxation bydisplacement flow-through of 1% sodium hydroxide solution at 90 C. forone minute, then rewashed. A. finishing wash was then given in watercontaining 0.1% S0 then centrifuged from an oil/water emulsion to leave0.2% of a controlled friction finish in the staple (Nopco RSF #18). Thestaple was then dried in a hot air steam.

Single filaments of this staple tested 4.0 grams per denier conditionedat 60% RH. and 75 F, 3.0 grams per denier wet and had an elongation of22.0% when conditioned by subjecting them to 60% relative humidity atfor a sufiicient time to bring the filaments to equilibrium. It wascarded and spun into 30s and 40s count yarn, then woven into a fabricwith ends/inch, and 80 picks/inch. The fabric was singed, desized,scoured and mildly bleached in conventional operations.

This fabric was subjected to a 50-cycle laundering evaluation alongsidecontrols of similar construction fabric made from cotton, regular rayon,commercial high strength tire yarn-type rayon, high wet-modulus rayon,etc.

Dimensional stability of the fibers of the invention were remarkablybetter than any of the other fibers tested as illustrated by valuesfound for fabric shrinkage. Whereas normal rayon showed a cumulativeshrinkage of 7%, commercial high tenacity tire cord type rayon 7l1%,high wet-modulus rayon 3-4%, cotton 2%, the fabric made from themulti-stage-stretch-and-relaxed fibers did not shrink, but showed a netpositive dimension change of +02%. Strength of fabric, toughness andabrasion resistance were higher for the rayon of this invention than forany of the other rayons tested both before and after laundering. Wetstrength was roughly equivalent to that for cotton even after the severelaundering, whereas hand was much superior.

Example I! An economical viscose composition containing 9.6% celluloseand 5.0% sodium hydroxide was prepared from Rayofiber-G wood pulpcellulose containing 96% alpha cellulose, having a cuene intrinsicviscosity 3.8, degree of polymerization of 750 and General Electricinstrument brightness of 93. The viscose was modified by addition of theregeneration retardants, spun under staple conditions, given multi-stageprimary stretch prior to regenerative fixing, converted into staple, andgiven relaxation in the manner outlined in Example I.

The finished single filament strengths were 3.8 grams per denierconditioned as in Example I, and 2.8 grams per denier wet with 21.0%elongation. The color of the filaments was somewhat whiter than thefilaments made in Example l, due to the pulp properties, and hadenhanced dyeing characteristics of faster exhaustion and deep shadedevelopment.

Fabric made therefrom with 45s count yarn in 136 x 64 constructionlaundered in a 50-cycle sequence alongside controls in identical fabricconstruction from fibers of cotton, regular rayon, etc., showedremarkably superior dimensional stability in the same order as fabricsof more open construction described in Example 1. Whereas no shrinkageoccurred in the fabric of the invention, other Example III Staple fiberproduced as described in Example I was spun into a 16s count yarn andWoven into a linen-type fabric at 50 ends/inch and 40 picks/inch.Following singeing, desizing, scouring and bleaching, this fabric wassubjected to a SO-cycle laundering sequence in comparison with severalsimilar fabrics made from cotton, normal rayon staple and highwet-modulus rayon. The launderability of the fabric of this inventionwas outstanding, with shrinkage of less than 1% compared with 2% forcotton, 8% for regular rayon and 4% for the high wet-modulus rayon. Wearcharacteristics, as shown by accelerated laboratory tests and actualextended use were very good for this rayon, much superior to either theregular or high wet-modulus rayons.

Example IV The 80 x 80 fabric of Example I was singed, desized anddried. This fabric was then padded with a solution containing 4% ofmethylated melamine resin with 15% MgCl .6H O catalyst (based on resinWeight) and 0.2%

v ly embrittled and unusable.

Example V Staple fiber of Example I was converted into 20s twoply yarnand knitted in mens socks using a 160-needle set-up. Following scouringand dyeing the socks were looped and boarded. These socks along withcomparable socks made from cotton, regular rayon, several commercialimproved rayons and high wet-modulus rayon were subjected to launderingand actual wear tests over a period of several weeks. The socks fromstaple fiber of this invention invariably performed in a very superiormanner compared with any of the other rayons, and were more or lessequivalent to the cotton socks in all regards including both sizestability and wear.

While not wishing to predicate the invention on any special theory, itis our belief that the production of fibers which can be converted intofabrics which are dimensionally stable during repeated severe launderingand exhibit no progressive shrinkage is based on the sequence ofprocessing embodying at least three essential steps: (1) high multistageprimary stretch while the fiber is in a semi-plastic and pliable stateprior to fixing-regeneration, (2) a hot acid regeneration step designedto completely fix the established oriented structure prior to anyrelaxation, and (3) complete relaxation through use of a swellingtreatment.

This application is a continuation-in-part of our application Serial No.848,512, filed October 26, 1959, and now abandoned.

We claim:

1. The improvement in the viscose process which comprises spinningviscose in an acid regenerating spin bath and stretching the filamentsat least 90% in a primary stage while in contact with spin bath, thencontacting the filaments which were not completely regenerated in theprimary stage with a hot acid bath containing from 1% to 6% of sulfuricacid while stretching the filaments an additional 5% to 50% tocompletely fix and regenerate the filaments. prior to any relaxation andthen subsequently immersing the filaments in an aqueous solutioncontaining a swelling agent at an elevated temperature while thefilaments are free to shrink to effect complete relaxation of thefilaments producing washable filaments having practically no shrinkageand which can be converted into yarns and woven fabrics which exhibitdimensional stability during repeated severe laundering.

2. The improvement in the viscose process defined in claim 1, whichcomprises incorporating a regeneration retardant in the viscose toproduce all-skin filaments, spinning the filaments in the primary stageat a temperature of from 40 to C. and fixing the filaments in thesecondary stage in acid bath at a temperature in the range of from to100 C.

3. The improvement in the viscose process defined in claim 2 in whichthe regeneration retardant is a physical mixture of about 0.2% each ofpolyethylene glycol and dirnethylamine.

4. The improvement in the viscose process defined in claim 1 in whichthe completely regenerated filaments are cut into staple fibers and saidstaple fibers are immersed into a solution containing from 0.1 to 2% ofsodium hydroxide for about one minute at a temperature of about C.

5. The improvement in the viscose process defined in claim 1 in whichthe swelling agent is a compound of the group consisting of sodiumhydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate,sodium sulfide and potassium thiocyanate in aqueous solution in amountsof about 1%, 1.4%, 0.6%, 10%, 3% and 3% respectively.

6. The improvement in the viscose process which comprises spinning theviscose in a hot acid spin bath and stretching the filaments at least90% while in contact with the spin bath or spin bath carryover toproduce filaments containing an appreciable portion of skin, thencontacting the filaments with a solution containing about 4% of sulfuricacid while stretching the filaments an additional 20% to eliminate theresidual xan'thate and effect complete regeneration, washing thefilaments, and then contacting the filaments at zero tension while freeto shrink with an aqueous swelling solution containing an alkali metalhydroxide at about 90 C. to eflect complete relaxation.

7. The improvement in the viscose process defined in claim 6 whichcomprises cutting the completely regenerated and washed filaments intostaple fibers and then immersing the staple fibers into a dilute sodiumhydroxide solution.

References Cited in the file of this patent UNITED STATES PATENTS2,491,938 Schlosser Dec. 20, 1949 2,611,928 Merion Sept. 30, 19522,952,508 Mitchell Sept. 13, 1960 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3,046,082 July 24, 1962 Reid LoganMitchell et al It is hereby certified that error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

Columnd, line 58, for "subject" read subjected column 3, llne 5, for"uesd" read used line 70, for

"steam" re ad stream column 4, line 1, for "75" read 75 F. column 5,line 7, for "useing" read using Signed and sealed this 6th day ofNovember 1962.

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents

1. THE IMPROVEMENT IN THE VISCOSE PROCESS WHICH COMPRISES SPINNINGVISCOSE IN AN ACID REGENERATING SPIN BATH AND STRETCHING THE FILAMENTSAT LEAST 90% IN A PRIMARY STAGE WHILE IN CONTACT WITH SPIN BATH, THENCONTACTING THE FILAMENTS WHICH WERE NOT COMPLETELY REGENERATED IN THEPRIMARY STAGE WITH A HOT ACID BATH CONTAINING FROM 1% TO 6% OF SULFURICACID WHILE STRETCHING THE FILAMENTS AN ADDITIONAL 5% TO 50% TOCOMPLETELY FIX AND REGENERATE THE FILAMENTS PRIOR TO ANY RELAXATION ANDTHEN SUBSEQUENTLY IMMERSING THE FILAMENTS IN AN AQUEOUS SOLUTIONCONTAINING A SWELLING AGENT AT AN ELEVATED TEMPERATURE WHILE THEFILAMENTS ARE FREE TO SHRINK TO EFFECT COMPLETE RELAXATION OF THEFILAMENTS PRODUCING WASHABLE FILAMENTS HAVING PRACTICALLY NO SHRINKAGEAND WHICH CAN BE CONVERTED INTO YARNS AND WOVEN FABRICS WHICH EXHIBITDIMENSIONAL STABILITY DURING REPEATED SEVERE LAUNDERING.